Unfortunately, it is still not possible to hardcode the Sql connection string - however, our development team will do its best to add it among the other improvements for the SharePoint web-parts for the Q1 2011 official release which is about a month away.
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!